Most semiconductor wafer processing fabricates multiple different areas on a wafer into identical circuitry which is subsequently cut from the wafer into individual chips or die. These are then fabricated into finished packages. One technique for cutting or singulating a wafer into individual die includes mechanical cutting with a diamond cutting wheel. One technique for holding the wafer during cutting includes use of a circular metal ring which is larger than the wafer being cut. A thin film, commonly referred to in the industry as cutting film, sticky backs or tape, is tightly spread over and across the metal ring. One side of the tape is provided to be tacky, while the opposing side is not. The tacky side is adhered to the ring. A surface of the wafer is substantially centrally positioned relative to the ring and adhered to the tacky side of the tape. With the wafer so adhered, the metal ring is then positioned relative to a cutting device which orients the holder and cuts the wafers along designated scribe lines or street areas on the wafer, where circuitry has typically not been fabricated, for separating the wafer into individual die.
The cut individual die remain attached to the tape due to the stickiness of the tape. Vacuum-type pick-and-place devices then engage individual selected die to pull such from the tape for positioning onto lead frames or other devices for incorporation into finished product. Testing of the individual die for operability is typically conducted prior to the cutting operation.
Unfortunately, the tacky nature of the tape is in some instances so great that the pick device can damage or fracture the die as it is being pulled from the tape. The problem is exacerbated with larger die.
One prior art technique of overcoming this problem utilizes a tape which upon exposure to ultraviolet light becomes less tacky. The ability to change the adhesive force on the tape allows for high adhesion during the wafer dicing operation, and then a lower adhesion during the die removal operation where the die are pulled from the tape. This reduces the force required for the die attach equipment to remove the die from the tape, yet provides maximum adhesion during the dicing operation. Certain ultraviolet light sensitive wafer tapes can provide an adhesion reduction factor of three or greater to achieve this purpose. The prior art exposes the entire back side of the tape stretched over the metal ring in achieving adhesion reduction. All of the die then become more loosely associated with the tape, such that picking and placing of the die can thereafter occur.